Method for estimating the position of a subscriber station of a radio communication system and network device

ABSTRACT

In a method for estimating the position of a subscriber station of a radio communication system, a receiver station receives reports from the subscriber station, said reports containing information relating to the signal strength of a receiving signal of at least one transmitting station in the locality of the subscriber station. The reports are stored in a memory of a network device of the radio communication system and a position determining unit takes into account at least two reports stored prior to the request for position estimation, in order to estimate the position of the subscriber station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to PCTApplication No. PCT/EP2004/051544 filed on Jul. 19, 2004 and GermanApplication No. 10345224.9 filed Sep. 29, 2003, the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method for estimating the position of asubscriber station of a radio communication system and a correspondingnetwork device.

Localizing subscriber stations in cellular networks has becomeincreasingly important in the past few years. On the one hand, there areregulations in some countries, whereby the operating companies are boundby law to determine the location of emergency calls. On the other hand,there is a commercializing of location-associated services at present,which requires a simple and cost-effective localizing of subscriberstations. There is a plurality of technical solutions in order toestimate the position of a subscriber station, the accuracy of which andthe cost of which vary. For example, the position of a subscriberstation can be determined with the help of an EOTD (Enhanced ObservedTime Difference) method, by the UTDOA (Uplink Time Difference ofArrival) or byby the AGPS (Assisted GPS). Either the installation ofadditional components in the radio access network or the use of specialsubscriber stations is required for this purpose.

On the one hand, many operating companies are not willing to make suchinvestments while, on the other hand, many applications do not require avery accurate determination of the position. That is why localizingmethods are particularly in demand, said methods being cost-effectiveand able to locate a subscriber station with an acceptable level ofaccuracy. However, the use of cell identification (cell ID) is notsufficient for this purpose. Only the inclusion of information inaddition to the cell identification permits the positioning ofsubscriber stations with an accuracy which is sufficient for mostapplications. One option for making available additional information isrepresented by the evaluation of the signal strengths of signalsreceived from a subscriber station. As a rule, the signal strengths ofreceive signals are used by the transmitting station, which providescoverage for a radio cell in which the subscriber station is located andby additional radio cells adjacent to the transmitting stations. Forexample, in GSM systems (GSM: Global System for Mobile Communications)each active mobile station reports every 480 ms about the signalstrength of receive signals of the base station covering them and aboutthe signal strengths of additional receive signals of up to six adjacentbase stations. These reports are compared with a signal strengthdatabase in order in this way to estimate the most likely location ofthe subscriber station in combination with the cell identification, ifrequired.

Such methods and systems are for example known from the internationalpatent application WO 98/15149.

Previously known methods for estimating the position of subscriberstations produce good results for estimating the position especially ifa plurality of reports of a subscriber station about signal strengths ofreceive signals is used at the same time for estimating the position.However, in a GSM system for example, when for example 10 reports aboutthe signal strengths of receive signals are used, there is an additionaldelay of approximately five seconds when determining the positions of asubscriber station.

From DE 100 56 22 A1, a method is known for localizing the traffic in acellular mobile telephony network, in which from the transitionprobabilities of a hidden Markov model and the observation probabilitiesof an interference model from a sequence of reports, a highly probablepath of a mobile subscriber can be determined. The reports contain thefield strength values of base stations measured by the mobilesubscriber. The reports are either sent directly to an arithmetic unitby the mobile subscriber or first collected by a base station and, ifrequired, supplemented by additional measured values and sent in theform of one complete message to the arithmetic unit.

SUMMARY OF THE INVENTION

One possible object of the invention relates to improving the estimationof the position with regard to the processing speed.

The inventors propose a method for estimating the position of asubscriber station of a radio communication system, a receiver stationreceives reports from the subscriber station, said reports containinginformation relating to the signal strength of a receive signal of atleast one transmitting station in the locality of the subscriberstation. The reports are stored in a memory of a network device of theradio communication system and a position determining unit takes intoaccount at least two reports stored prior to the request for positionestimation in order to estimate the position of the subscriber station.

The method makes it possible that, on submission of a request forestimating the position of a subscriber station, reports withinformation about the signal strengths of receive signals canimmediately be read from the memory and delivered to the positiondetermining unit. Therefore, position estimation can be carried outwithout an additional time delay. Information about the signal strengthof a receive signal is for example the signal strength of the receivesignal or a parameter from which the signal strength can be derived.

In a preferred embodiment, the receiver station is used as the networkdevice. The continuously stored reports about the subscriber stationfrom the receiver station, for example the base station, which providescoverage for the radio cell in which the subscriber station is located,are for example used to make a decision about the handover to adjacentbase stations. The reports are only signaled to the position determiningunit if there is a request to determine the position of the subscriberstation, i.e. the signaling load occurring in the radio communicationsystem as a result of the reports is minimal.

Advantageously, during an active connection, the reports are receivedand/or stored regularly at specific time intervals in an idle mode ofthe subscriber station. A number of reports required for estimating theposition can be requested at any time from the memory as a result ofthem being received at regular intervals.

It is advantageous if a maximum of a first number of reports is storedin the memory. The memory space used for reports can be selected in sucha way that it can store only the first number of reports, for example,those reports that are used as a maximum number by the positiondetermining unit in order to estimate the position can be stored. If thememory is full, the oldest report will be replaced with the next reportreceived from the subscriber station. In this way, in the case of a fullmemory, the most up-to-date reports are always available in the memory.

In a further development, the position determining unit requests asecond number of reports from the network device. This has the advantagethat the position determining unit can determine the second number ofreports depending on the accuracy required for estimating the position.

A preferred further development provides that the network device, if atthe time of the request it has stored a smaller number of reports thanthe second number of reports, stores additional reports until the secondnumber of reports has been stored or until a maximum period of time hasexpired and either prior to the expiry of the maximum period of time ofthe second number of reports or after the expiry of the maximum periodof time sends the number of reports stored upon that time to theposition determining unit, even if the set of stored reports remainssmaller than the second number of reports.

The further development makes it possible that, reports are sent to theposition determining unit at the latest after the maximum period of timehas expired. Therefore, the time required for estimating the position islikewise limited to a maximum value.

Advantageously, the position determining unit carries out the estimationof the position by comparing the signal strengths given in the reportswith a signal strength database in accordance with WO 98/15149.

It is advantageous if, in addition, the transmitting power is given inthe reports, by which at least one transmitting station has sent thereceive signal in each case. Signals on signaling channels, for example,broadcasting channels, are usually sent at any time with a transmittingpower that is well-known in the radio communication system and constant,and received by subscriber stations. From the transmitting power on thesignaling channels known in particular by the position determining unitand the signal strength of the receive signal which can be taken fromthe reports, it is in this way also possible to calculate and take intoaccount the signal attenuation for estimating the position. As a resultof the fact that in the reports, the transmitting power by which thereceive signal was sent is in addition given, it is in this way alsopossible to take into account the signal strength of the receive signalfor estimating the position if the receive signal was received on atraffic channel with a transmitting power control, i.e. on a channelwith a continuously varying transmitting power.

Advantageously, as additional information about estimating the position,the reports can in each case be supplemented by the transmitting powerof the subscriber station and the corresponding receive power at thereceiver station receiving the reports.

The network device proposed by the inventors has all the requiredfeatures for carrying out the method.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 shows a schematic diagram of an exemplary embodiment forestimating the position of a subscriber station of a radio communicationsystem and

FIG. 2 shows a schematic diagram of a first sequence of occupancy of amemory with reports during the implementation of the method inaccordance with FIG. 1,

FIG. 3 shows a schematic diagram of a second sequence of occupancy of amemory with reports during the implementation of the method inaccordance with FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

A subscriber station is for example a mobile telephone, even a portable,or a fixed device for the transmission of video and/or audio data, forsending faxes, sending Short Message Service messages SMSs and forsending e-mails and also for access to the Internet.

A receiver station is for example a subscriber station or a basestation. Below, a base station is regarded as the receiver station,however without being limited thereto.

A transmitting station is for example a subscriber station or a basestation. Below, a base station is regarded as the transmitting station,however without being limited thereto.

The method can advantageously be used in any radio communicationsystems. Radio communication systems mean any systems in which data canbe transmitted between stations via a radio interface. The transmissionof data can be both bidirectional and unidirectional. Radiocommunication systems are in particular any mobile radio systems forexample in accordance with the GSM standard or the UMTS (UniversalMobile Telecommunication System) standard. Radio communication systemsalso mean future mobile radio systems for example of the fourthgeneration.

The method is described below using a mobile radio system in accordancewith the GSM standard as a basis, however without being limited thereto.

FIG. 1 shows a schematic diagram of a radio communication system. Afirst base station BS1 supplies a radio cell FZ. The first base stationBS1 is connected to a base station controller BSC. The base stationcontroller BSC is connected to a core network via connections which arenot shown. Via this hidden core network, external position determiningservices (LCS: Location Services) can send a request for estimating theposition of a subscriber station via the base station controller BSC toa position determining unit SMLC, which as a result carries out theposition estimation for the subscriber station.

In the radio cell FZ of the first base station BS1 there is a subscriberstation MS with a transmitter and a receiver unit SE for transmittingand receive signals. Irrespective of whether or not a positionestimation is carried out for the subscriber station MS or whether thereis a request for estimating the position, the subscriber station MScontinuously receives first receive signals S1 from the first basestation BS1, second receive signals S2 from a second base station BS2,third receive signals S3 from a third base station BS3 and fourthreceive signals S4 from a fourth base station BS4 and specifically forthe four receive signals S1, S2, S3, S4 in each case a signal strength,i.e. a transmitting power of the receive signals S1, S2, S3, S4. Thefour receive signals S1, S2, S3, S4 are for example the signals ofbroadcasting channels on which the base stations BS1, BS2, BS3 and BS4send for example information about their specific radio cell with atransmitting power, which is constant and known in the radiocommunication system. The receive signals S1, S2, S3, S4 can be receivedby the subscriber station MS both during an active connection with thefirst base station BS1 and in the idle mode. The subscriber station MStransmits information relating to the signal strengths of the receivesignals S1, S2, S3, S4 at regular intervals for example every 480 ms asreports B1, B2, B3, B4, B5, B6, B7, B8, B9, B10 to the first basestation BS1. The first base station BS1 stores the reports B1, B10received by the subscriber stations MS in a memory SP.

Each report B1, B10 contains at least information relating to the signalstrength of one of the four receive signals S1, S2, S3, S4. Preferably,each report contains information relating to the four receive signalsS1, S2, S3, S4. The information, for example, explicitly gives thesignal strength (receive power) of the specific receive signal or makespossible a calculation of the specific signal strength.

If the subscriber station MS, for example, receives the first receivesignal S1 of the first base station BS1 on a traffic channel, which hasa transmit power control, the subscriber station MS transmits in thereports B1, B10 in addition to the information relating to the signalstrength of the first receive signal S1, also the associatedtransmitting power, by which the first base station BS1 has transmittedthe first receive signal S1 in each case. The transmitting power of thefirst receive signal S1 is sent to the subscriber station MS for examplefrom the first base station BS1 or can be calculated on the basis of thesignal attenuation determined by it from signals received on thebroadcasting channel of the first base station BS1. As an alternative,the first base station BS1 can even supplement the reports B1, B10received from the subscriber station MS by its specific transmittingpower. Information about the transmitting power of the receive signal ofthe first base station BS1 in the reports B1, B10 is effective whenusing a traffic channel in order to be taken into account in combinationwith the associated signal strength (receive power) of the receivesignal for estimating the position of the subscriber station MS.

The base station controller BSC receives, for example, from an externalunit EXT, for example an external position determining service, via thecore network, which is not shown, a request AUF for estimating theposition of the subscriber station MS. The request AUF is forwarded bythe base station controller BSC to a position determining unit SMLC. Asa result, the position determining unit SMLC initiates the positionestimation of the subscriber station MS and requests from the first basestation BS1, for example, ten reports about the signal strengths ofreceive signals. That is why the first base station BS1 subsequentlytransmits the ten reports B1, B10, which are available at the time ofthe request by the position determining unit SMLC in its memory SP, viathe base station controller BSC to the position determining unit SMLC.By comparing the signal strengths of the receive signals which can betaken from the reports B1, B10 with a signal strength database, theposition determining unit SMLC caries out a position estimation andtransmits the estimated position to the external unit EXT

For example, in the signal strength database, for a plurality oflocations within the radio cell FZ of the first base station BS1, signalstrengths or signal attenuations for signals from the first base stationBS1 and from adjacent base stations, for example, from the second, thirdand the fourth base station BS2, BS3 and BS4 are stored. By comparingthe signal strengths (or the calculated signal attenuations arising fromthese) measured by the subscriber station MS with the signal strengthdatabase, the location with the best correlation is established anddetermined as the estimated position.

In addition to the comparison of the signal strengths with the signalstrength database, which can be taken from the reports B1, B10, theposition determining unit SMLC can of course also include additionalinformation about estimating the position. This additional informationalso includes for example the cell identification of the first basestation BS1 allocated to the subscriber station MS, in the radio cell FZof which the subscriber station has checked-in or also corrects thetiming advance referred to in this way, i.e. the correction factor bywhich the subscriber station MS corrects its transmission points intime. The timing advance is sent to the subscriber station MS from thefirst base station BS1. The first base station BS1 determines the timingadvance from the round-trip time of a signal from the first base stationBS1 to the subscriber station MS and back. The current value of thetiming advance can be added in each case by the first base station BS1to the reports B1, B10 received from the respective subscriber stationMS.

If, as shown in FIG. 1, the number of reports requested by the positiondetermining unit SMLC at the point in time of the request AUF hasalready been stored in the memory SP of the first base station BS1, thissaid number of reports is immediately made available to the positiondetermining unit SMLC and a position is therefore determined withoutadditional delays.

FIG. 2 schematically shows an additional embodiment, which illustratesan alternative timing sequence of the occupancy of the memory SP for theradio communication system shown in FIG. 1.

At a first point in time t1, the position determining unit SMLC requeststen reports from the first base station BS1. However, at this firstpoint in time t1 only four reports B1, B2, B3, B4 are stored in thememory SP. That is why the first base station BS1 waits to transmitreports to the position determining unit SMLC and, in addition, storesthe reports from the subscriber station MS. At a second point in timet2, an additional six reports B5, B6, B7, B8, B9, B10 have arrived andbeen stored in the first base station BS1. As a result, the first basestation BS1 transmits all ten the reports B1, B10 to the positiondetermining unit SMLC.

The period of time between the request for the ten reports by theposition determining unit SMLC and the delivery of the ten reports B1,B10 from the first base station BS1 to the position determining unitSMLC is obtained from the difference between the two points in timet2-t1. In this embodiment, this period of time t2-t1 is smaller than amaximum period of time t_max, which expires at a third point in time t3and thus has a duration of t3-t1. As a result, the first base stationBS1 can still prior to the expiry of the maximum period of time, deliverthe ten reports B1, B10 to the position determining unit SMLC. Themaximum period of time t_max determines the period of time within whichthe first base station BS1 has to deliver reports to the positiondetermining unit so that the total time for estimating the position,i.e. the time which has expired from the moment of the request AUF forestimating the position up to provision of the information about anestimated position, does not exceed a maximum total time. For example,the position determining unit SMLC specifies the maximum period of timet_max for the first base station BS1.

In a third embodiment shown schematically in FIG. 3, at a first point intime t1, four reports B1, B2, B3, B4 are stored in the memory SP. At thethird point in time t3, i.e. after expiry of the maximum period of timet_max, only a total of eight reports B1, B8 are stored in the memory SRIn this case, the first base station BS1 no longer waits for additionalreports from the subscriber station MS in order to prevent the totaltime for estimating a position from becoming too long. That is why inthis embodiment, it delivers only the eight reports to the positiondetermining unit SMLC instead of the ten reports. This results in theestimation of the position by the position determining unit SMLCpossibly being more inexact than would be the case with the ten reports,but estimating the position in this way is always carried out within amaximum total time. The value of the maximum period of time t_max can bedetermined by the position determining unit SMLC or another networkdevice, for example, depending on the nature of the position determiningservice, which transmits the request AUF for estimating the position ofthe subscriber station MS.

A request for estimating the position of a subscriber station MS can ofcourse not only be generated by the external unit EXT, but also by theradio communication system, for example, by the subscriber station MS,by a switching center (MSC: Mobile Switching Center), by a GatewayMobile Location Center (GMLC) or also by the position determining unitSMLC.

Further additional information, which can be used by the positiondetermining unit SMLC in addition to the cell identification of theradio cell FZ of the first base station BS1 in order to improve theposition estimation of the subscriber station MS, is the currenttransmitting power by which the subscriber station MS in each case sendsits reports B1, B10 to the first base station BS1, together with thecorresponding receive power of the reports B1, B10. This additionalinformation is for example added to the reports B1, B10 of thesubscriber station MS by the first base station BS1.

The memory SP of the first base station BS1 can for example be a memory,which stores a maximum set of ten reports and on the arrival of theeleventh report deletes the first report and in this way replaces theoldest report with the eleventh report. In this way, only the most up todate ten reports are always stored in the memory SP. This maximum set ofstored reports corresponds, for example, to that number of reports,which are requested to the maximum by the position determining unit SMLCfor estimating a position. The memory SP can of course be arranged bothin the first base station BS1 and in another network device of the radiocommunication system, for example, in the base station controller BSC orin the position determining unit SMLC. As a matter of course, the memorySP can also be arranged in the subscriber station MS. Only after thereports have been requested, said reports are transmitted upon that timevia the first base station BS1 to the position determining unit SMLC.

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention covered by the claims which may include thephrase “at least one of A, B and C” as an alternative expression thatmeans one or more of A, B and C may be used, contrary to the holding inSuperguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).

1-10. (canceled)
 11. A method for estimating the position of asubscriber station in a radio communication system, comprising:receiving reports from the subscriber station at a receive station, eachreport containing information relating to a signal strength at alocation of the subscriber station of at least one receive signalreceived by the subscriber station and sent by a transmitting station;storing the reports in a memory of a network device of the radiocommunication system; receiving a request for position estimation at theradio communication system; and estimating the position at a positiondetermining unit taking into account at least two reports stored priorto the request for position estimation.
 12. The method according toclaim 11, wherein the receive station is used as the network device. 13.The method according to claim 11, wherein the reports are receivedand/or stored regularly at specific time intervals.
 14. The methodaccording to claim 11, wherein the reports are received and storedregularly at specific time intervals, and the reports are received andstored during both an active connection and in an idle mode.
 15. Themethod according to claim 11, wherein the memory stores a first numberof reports as a maximum.
 16. The method according to claim 11, whereinthe position determining unit requests a second number of reports fromthe network device.
 17. The method according to claim 16, wherein if thenumber of reports stored is fewer than the second number when therequest for position estimation is received, then the network devicestores additional reports until the second number of reports has beenstored or until a maximum period of time has expired, if the secondnumber of reports is stored before expiration of the maximum period oftime, then the network device sends the second number of reports priorto the expiry of the maximum period of time, and if the second number ofreports cannot be stored before expiration of the maximum period oftime, then the base station sends all stored reports after the expiry ofthe maximum period of time, even if the number of stored reports remainssmaller than the second number of reports.
 18. The method according toclaim 11, wherein the position determining unit estimates position bycomparing signal strengths obtained from the reports with signalstrengths stored in a signal strength database.
 19. The method accordingto claim 11, wherein each report also contains information relating to atransmitting power used to transmit the at least one receive signal. 20.The method according to claim 11, wherein the reports also contain: atransmitting power used by the subscriber station to transmit the reportto the receive station, and a receive power at which each report wasreceived by the receive station in each case].
 21. The method accordingto claim 12, wherein the reports are received and stored regularly atspecific time intervals, and the reports are received and stored duringboth an active connection and in an idle mode.
 22. The method accordingto claim 21, wherein the memory stores a first number of reports as amaximum.
 23. The method according to claim 22, wherein the positiondetermining unit requests a second number of reports from the networkdevice.
 24. The method according to claim 23, wherein if the number ofreports stored is fewer than the second number when the request forposition estimation is received, then the network device storesadditional reports until the second number of reports has been stored oruntil a maximum period of time has expired, if the second number ofreports is stored before expiration of the maximum period of time, thenthe network device sends the second number of reports prior to theexpiry of the maximum period of time, and if the second number ofreports cannot be stored before expiration of the maximum period oftime, then the base station sends all stored reports after the expiry ofthe maximum period of time, even if the number of stored reports remainssmaller than the second number of reports.
 25. The method according toclaim 24, wherein the position determining unit estimates position bycomparing signal strengths obtained from the reports with signalstrengths stored in a signal strength database.
 26. The method accordingto claim 25, wherein each report also contains information relating to atransmitting power used to transmit the at least one receive signal. 27.The method according to claim 26, wherein the reports also contain: atransmitting power used by the subscriber station to transmit the reportto the receive station, and a receive power at which each report wasreceived by the receive station in each case].
 28. A network device fora radio communication system, comprising: a memory for storing thereports, which a receive station has received from a subscriber station,in which the reports in each case contain information relating to asignal strength at a location of the subscriber station of at least onereceive signal received by the subscriber station and sent by atransmitting station; a transmitter to transmit, after a request forposition estimation has been received at the radio communication system,at least two reports stored prior to receiving the request for positionestimation, the reports being transmitted to a position determiningunit, in which the position is estimated taking into account the atleast two reports; and a controller to control the network device sothat at least two reports are stored prior to the request for positionestimation.